Spruce top cupped

[Jim88]

Hello all,,

I had joined my first soundboard together and thicknessed it to just over 3mm,,
The soundboard had been sitting for a week while i was waiting for wood to Cut a rossette,,
All was going well i was actually pretty pleased as its my first top,,then one morning i checked the top and it was extremely concave/convex , more than the back of a guitar,,,so i had a little "flex" and it cracked slightly at the join,,,

Ive broke the joint and straitened the wood and its ready for next attempt,,or,,,

Forgive my inexperience i am just baffled as to why in 1 night after being joined and perfectly flat for a week,,it would bend like that?

I am naively putting it down to either my girlfriend opening a window in the morning and changing the humidity in the room,,or the wood being fresh and not dry enough, as it was a cheap top ,as i am using my first build just to get organised with what tools etc i can get away with,,

Anyone had this happen before or could explane,,?

I knew humidity levels were important but i must have underestimated them,,,

Thanks,,,

[Ned Milburn]

Originally Posted by Jim88

Hello all,,

I had joined my first soundboard together and thicknessed it to just over 3mm,,
The soundboard had been sitting for a week while i was waiting for wood to Cut a rossette,,
All was going well i was actually pretty pleased as its my first top,,then one morning i checked the top and it was extremely concave/convex , more than the back of a guitar,,,so i had a little "flex" and it cracked slightly at the join,,,

Ive broke the joint and straitened the wood and its ready for next attempt,,or,,,

Forgive my inexperience i am just baffled as to why in 1 night after being joined and perfectly flat for a week,,it would bend like that?

I am naively putting it down to either my girlfriend opening a window in the morning and changing the humidity in the room,,or the wood being fresh and not dry enough, as it was a cheap top ,as i am using my first build just to get organised with what tools etc i can get away with,,

Anyone had this happen before or could explane,,?

I knew humidity levels were important but i must have underestimated them,,,

Thanks,,,

Do you know your room humidity??

When did you buy the wood??

How long did it acclimatize before working on it??

If wood is not fully dried and acclimatized to the building environment's RH, and if it is placed one face down, the face up side will usually dry out first, shrinking and cupping. Flip it over for a couple days and see if it reverts to normal.

[charles Tauber]

Originally Posted by Jim88

opening a window in the morning and changing the humidity in the room

That'll do it.

Thin, wide pieces of wood will respond to humidity changes fairly rapidly, particularly if one face is exposed and the other not. Constant relative humidity is needed to have stable geometry while making and assembling guitar parts.

[Jim88]

The wood was standing verticle with all both sides exposed,,each morning i would turn it also, i never had it face down on the bench,,

[charles Tauber]

Originally Posted by Jim88

The wood was standing verticle with all both sides exposed,,each morning i would turn it also, i never had it face down on the bench,,

It is quarter sawn?

[Jim88]

Yeap it is nicely quater sawn,,it was looking really nice straight,,

Like i said i was keeping a eye on it for a week and was straight not bent at all ,,then in the space of a night it was like a square satilite dish